U.S. Pat. Nos. 4,584,439 and 4,903,308, and pending U.S. patent application Ser. Nos. 07/499,492 filed Mar. 29, 1990; 07/436,914 filed Nov. 14, 1989; 07/708,924 filed Apr. 11, 1991; and 07/730,172 filed Jul. 12, 1991, are incorporated herein by reference, as they disclose variations and refinements of an audio transducer having a diaphragm that can be generally described as "cylindrical" in the broadest sense of the term. That is, the diaphragm is defined by a two-dimensional cross-sectional profile that is projected on an axis to form a three-dimensional diaphragm having a constant cross-section. The cross-sectional profile need not be circular but may be an open or closed polygon or curve. These cylindrical diaphragms may generally be formed from flat sheets that are curved so that all lines normal to the curved surface remain perpendicular to the axis of projection. The diaphragms in the disclosed patents typically include a pair of tangentially abutting circular or semi-circular cross-sectional tube-shaped webs.
In operation, these cylindrical diaphragm transducers generate sound by a "rolling motion" in which an electromagnetic coil attached to the diaphragm interacts with a fixed magnetic field to move in a direction perpendicular to the axis of projection of the diaphragm. Each of various portions of the diaphragm accommodate the coil motion relative to a fixed frame by selectively tightening and loosening its radius of curvature to achieve the rolling motion.
While the transducers of the above-referenced applications and patents are reasonably efficient, with a relatively flat frequency response over a large bandwidth of approximately 5 octaves, there remains a need for additional improvements in the performance criteria of efficiency, bandwidth and response flatness. In addition, there is a need to reduce manufacturing costs and to further increase product quality by simplifying the manufacture of such a device.